Optical coherence tomography (OCT) is a method for investigating light scattering specimens. Biological tissue is particularly suitable for investigation by means of OCT due to its light-scattering properties. Since OCT only requires relatively low light intensities and the wavelengths of the light used mainly come within the near infrared range (750 nm to 1350 nm), it does not—unlike X-ray diagnostics—subject the biological tissue to any radiation.
Therefore, OCT is particularly significant for medicine and is comparable to ultrasound diagnostics, instead of noise, however, broadband light with a very short coherence length being used. The life spans of the light reflected on different boundary layers in the specimen are recorded with the aid of an interferometer. By means of OCT one can typically achieve resolutions one to two orders of magnitude higher than with ultrasound, however the maximum measuring depth is considerably smaller. Due to optical scattering the cross-sectional images obtained only reach to a depth of a few millimeters into the tissue. The currently most important fields of application for OCT are in opthalmology, dermatology and the diagnosis of cancer. However, there are also non-medical applications, such as e.g. materials testing.
It is known from Y. Watanabe et al., OPTICS COMMUNICATIONS 261 (2006) 376-380 and Y. Watanabe et al., APPLIED OPTICS Vol. 44, No. 8 (2005) 1387-1392 to record two-dimensional interference images from a specific depth of a specimen with different phase differences between the specimen and reference arm of the interferometer with a two-dimensional camera, and to calculate a two-dimensional image from this. An actuator adjusts the optical path length of a path of an optical interferometer. With a first position a measuring point is recorded. After this the path difference is changed, and a second measuring point recorded. A third measuring point is obtained in a similar way. The amplitude of the OCT signal is calculated from these three measuring values. With this method it cannot always be guaranteed that the image information from the inside of the specimen produced from the interference images obtained in this way have the quality required with specific diagnostic applications. Moreover, with this method very fast movement of the actuator is required in order to be able to avoid blurs caused by possible movement of the specimen. Moreover, very long down times result during which no images can be recorded.
An OCT method is known from US 2004/0263859 A1 wherein a tomogram of a specific layer within a body is established from a non-interference image (Id) of a background and two interference images (I0, IΦ) recorded with different phase positions. In order to reduce noise, the two interference images (I0, IΦ) recorded with different phase positions are respectively obtained by averaging a number of interference images recorded at different times. With this method a high image quality of the tomogram obtained can not be guaranteed in all applications.